docs: def _get_ctypes(self):
          """
          Returns all related objects for this model.
          """
          ctypes = []
          for related_object in self.model._meta.get_all_related_objects():
              model = getattr(related_object, 'related_model', related_object.model)
              ctypes.append(ContentType.objects.get_for_model(model).pk)
              if model.__subclasses__():
                  for child in model.__subclasses__():
                      ctypes.append(ContentType.objects.get_for_model(child).pk)
          return ctypes